This invention relates to a method for performing electrochemical fine processing of a surface of a material such as metal or semiconductor or the like.
In the prior art, when the fine processing of the surface of such a material is performed, a technique called photolithography has been generally used. The outline of this technique is shown in FIGS. 6A-6G.
At first, a resin (photoresist) 22 having photosensitivity and resistance to chemicals is applied on the surface of an article 21 to be processed (FIGS. 6A and 6B), and is irradiated with ultraviolet light through a mask 23 (FIGS. 6C and 6D). Next, the photoresist 24 which has been sensitized is removed by development and rinsing, allowing photoresist to remain on the article 21 to be processed exactly in accordance with a pattern drawn on the mask, while the other portions are exposed (FIG. 6E). Then, in this method, by immersion in a solution (etching solution) capable of dissolving the article 21 to be processed, the exposed portions of the article 21 to be processed are selectively removed (FIGS. 6F and 6G).
In addition, a technique is also used in practice in which no mask is used, and an electron beam the article to be processed is provided with a photoresist layer and is directly irradiated so as to form a pattern on the photoresist. At this time, it is also possible to produce a structure having a high aspect ratio by selecting an etching solution.
As another fine processing technique, there is the recently developed LIGA process. The outline of this process is shown in FIGS. 7A-7D. In FIG. 7A, X-rays emitted from a synchrotron (synchrotron emission light) are used to perform patterning of a resist 26 which may be made of acrylic, polymethylmethacrylate (PMMA) or the like thickly applied on the surface of a metal substrate 25 via a mask 27. In FIG. 7B, the exposed resist is removed by development and rinsing, and remaining portions of the resist 26 are used as a casting mold. In FIG. 7C, a metal 28 is deposited in the mold by means of electrocasting or the like. In FIG. 7D, the mold formed by the resist 26 is removed and then a fine metal structure 28 is obtained on the metal substrate 25.
Synchrotron emission light has characteristics such that the beam intensity is high, the linearity is strong and the divergence is small so that it becomes possible to accurately and deeply sensitize a mask pattern into a thickly applied resist. Therefore, when this technique is used, a fine three-dimensional shape having a high aspect ratio can be obtained.
However, in the conventional photolithography, there has been a problem that because the photomask is a flat glass substrate, when the article to be processed has an excessively uneven portion thereon, a gap is created between the photomask and the article to be processed, causing diffraction of ultraviolet light, so that it becomes difficult to accurately transfer the pattern of the mask onto the photoresist. In addition, in order to uniformly apply the photoresist onto the article to be processed, a technique called spin-coating utilizing centrifugal force is used, so that there is also a problem that when there is a level difference on the surface, uniform application of the photoresist becomes difficult. Also when the resist is directly irradiated with an electron, there is a problem of focusing the electron beam, so that it is difficult to perform patterning of a surface having complex irregularities. Further, the LIGA process must use a synchrotron, resulting in the problem of a costly apparatus.